From Teacher Workshop to Self-Study Online Module: Developing a Video-Based Resource for Diagnostic Accuracy in Primary Mathematics Teacher Education

Diagnostic competence is central to primary mathematics teacher education but existing approaches tend to depend on individual personnel and module structures, limiting their sustainability. This study combines a research-informed design approach with quasi-experimental intervention cycles: a fully asynchronous, video-based Moodle self-study module was developed to foster diagnostic competence in early arithmetic, consistently grounded in an empirically validated cognitive-developmental model. The module was implemented and iteratively refined across four phases—an in-service teacher workshop, a module pilot, and two quasi-experimental intervention cycles with pre-service primary teachers, including matched control groups. Across phases, the most consistent finding was a significant pre–post improvement in diagnostic accuracy for a below-average-performing pupil profile in the intervention group, while effects for average- and above-average profiles were less uniform. Log-data analyses showed that actual engagement with video vignettes, rather than structural completion, was the active ingredient of learning gains. Three design principles are proposed: model-based mathematical design, vertical connection of in-service and pre-service contexts, and guided asynchronous self-study with structured feedback. The study provides promising, context-bound evidence that a theoretically grounded, personnel-independent digital module can be integrated sustainably into primary teacher education and can foster diagnostic accuracy under the institutional and sample conditions investigated, while yielding initial design knowledge for comparable development efforts.